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TR.31.2.20 Turkish Seismic Code

This set of commands may be used to define the parameters for generation of equivalent static lateral loads for seismic analysis per the specifications laid out in Specification for Structures to be Built in Disaster Areas Part – III – Earthquake Disaster Prevention Amended on 2.7.1998, Official Gazette No. 23390 (English Translation). This is referred to as the Turkish Seismic Provisions.

The seismic load generator can be used to generate lateral loads in the X & Z directions for Y up or X & Y for Z up. Y up or Z up is the vertical axis and the direction of gravity loads (See the SET Z UP command in TR.5 Set Command Specification). All vertical coordinates of the floors above the base must be positive and the vertical axis must be perpendicular to the floors.  

General Format

STAAD utilizes the following format to generate the lateral seismic loads.

DEFINE TURKISH LOAD
tur-spec
weight-data

Refer to Common Weight Data for information on how to specify structure weight for seismic loads.

Where:

tur-spec = { A f1 TA f2 TB f3 I f4 RX f5 RZ f6 (CT f7) (PX f8) (PZ f9) } 
ParameterDescription
A f1 Effective Ground Acceleration Coefficient, Ao. Refer table 6.2
TA f2 Spectrum Characteristic Periods, TA and TB. These are user input and found in Table 6.4
TB f3 Spectrum Characteristic Periods, TA and TB. These are user input and found in Table 6.4
I f4 the earthquake importance factor of the structure.
RX f5 Structural Behavior Factors (R) along X and Z directions respectively. These are user input and please refer Table 6.5
RZ f6 Structural Behavior Factors (R) along X and Z directions respectively. These are user input and please refer Table 6.5
CT f7 Optional CT value to calculate time period. See section 1617.4.2.1, equation 16-39 of IBC 2000 and section 9.5.5.3.2, equation 9.5.5.3.2-1 of ASCE 7-02.
PX f8 Optional Period of structure (in sec) in X-direction to be used as fundamental period of the structure instead of the value derived from section 1617.4.2 of IBC 2000, and section 9.5.5.3 of ASCE 7-02.
PZ f9 Optional Period of structure (in sec) in Z-direction to be used as fundamental period of the structure instead of the value derived from section 1617.4.2 of IBC 2000, and section 9.5.5.3 of ASCE 7-02.
WEIGHT w joint weight associated with list
UNI v1 v2 v3 Used when specifying a uniformly distributed load with a value of v1 starting at a distance of v2 from the start of the member and ending at a distance of v3 from the start of the member. If v2 and v3 are omitted, the load is assumed to cover the entire length of the member.
CON v4 v5 Used when specifying a concentrated force with a value of v4 applied at a distance of v5 from the start of the member. If v5 is omitted, the load is assumed to act at the center of the member.
PRESSURE p1 weight per unit area for the plates selected. Assumed to be uniform over the entire plate.

Element Weight is used if plate elements are part of the model, and uniform pressures on the plates are to be considered in weight calculation.

Floor Weight is used if the pressure is on a region bounded by beams, but the entity which constitutes the region, such as a slab, is not defined as part of the structural model. It is used in the same sort of situation in which one uses FLOOR LOADS (See TR.32.4.3 Floor Load Specification for details).

Note: For additional details on the application of a seismic load definition used to generate loads, refer to GUID-6D9B5C48-9FFF-4548-BFB4-ACAE1E973743.

Base Shear

The minimum lateral seismic force or base shear, Vt, is automatically calculated per equation 6.4 in section 6.7.1:

V t = W A ( T 1 ) R a ( T 1 )
where
T1
=
the fundamental time period of the structure

Except that Vt shall not be less than:

V t , min = 0.10 A 0 I W

Seismic Load Reduction Factor, Ra (T1), in above equation is determined based on the following equations 6.3a and 6.3b in the code:

R a ( T 1 ) = 1.5 + ( R 1.5 ) T 1 T a when 0 T 1 T a R when T 1 > T a

The Structural Behavior Factor in either direction, RX and RZ, are provided through user input (variables f5 and f5) along the direction of calculation. Spectrum Characteristics Period, TA and TB, are also provided by user through the parameters (variables f2 and f3).

where
Ra
=
the Structural Behavior Factor in either direction, RX and RZ, are provided through user input (variables f5 and f5) along the direction of calculation
Ta, Tb
=
the Spectrum Characteristics Period are provided by user through the parameters (variables f2 and f3)
T1
=
the fundamental Lateral period in the direction under consideration and is determined as:
  1. Calculated by the empirical formulae as described below provided hn is in meter:

    T1 = CT [hn] ¾

    Where CT is assumed to be 0.075 for steel moment frames, 0.085 for concrete moment frames, or any user specified value.

  2. The period is also calculated in accordance with the Rayleigh method but could be overridden by user specified time period (PX, PZ).

The time period calculated based on method (a) is used in further calculation unless it is greater than 1.0 sec and 1.3 times of this is greater than the same calculated based on method (b). In that case time period calculated based on method (b) is used.

A(T1)
=
the Spectral Acceleration Coefficient is determined as follows as per eq. 6.1,

A(T1) = Ao I S(T1)

Ao and I
=
in above equation are Effective Ground Acceleration Coefficient and Building Importance Factor are provided by the user through the load definition parameter and could be found in table 6.2 and 6.3 respectively in the code
S(T1)
=
the Spectrum Coefficient is found by following equations, could be found in eq. 6.2a, 6.2b and 6.3c in original code
S ( T 1 ) = 1 + 1.5 T 1 T A when 0 T < T A 2.5 when T A T T B 2.5 ( T B T 1 ) 0.8 when T B < T
W
=
the weight of the building and shall be calculated internally using the following formula:
W = i = 1 n W i
Wi
=
the portion of W that is located at or assigned to level i

Vertical Distribution

As per 4.1.8.11(6), the total lateral seismic force, Vt, shall be distributed such that a portion, Ft shall be concentrated at the top of the building, where,

ΔFN = 0.07 T1 Vt

  • but ΔFN is not greater than 0.20Vt
  • and ΔFN = 0 when HN ≤ 25 m.
The remainder (V- ΔFN), shall be distributed along the height of the building, including the top level, in accordance with the following formula (per equation 6.9:

Fi = (Vt - ΔFN ) wi Hi / Σ wj Hj

where
Fi
=
the lateral force applied to level i
ΔFN
=
the portion of Vt to be concentrated at the top of the structure
Wi, Wj
=
the portion of W that is located at or assigned to level i or j respectively
i
=
level i is any level in the building, i = 1 for first level above the base.
N
=
level N is uppermost in the main portion of the structure

Example

DEFINE TUR LOAD
A 0.40 TA 0.10 TB 0.30 I 1.4 RX 3.0 RZ 3.0 
SELFWEIGHT
JOINT WEIGHT
17 TO 48 WEIGHT 7
49 TO 64 WEIGHT 3.5
LOAD 1 EARTHQUAKE ALONG X
TUR LOAD X 1.0
PERFORM ANALYSIS PRINT LOAD DATA
CHANGE